Resilient friction material

ABSTRACT

A blocker-clutch assembly (10) includes an openly porous, pyrolytic carbon composite friction material (74) configured for optimum performance and, therefore, prevention or substantial prevention of nonsynchronous engagement of positive clutch members (12,14) due to premature unblocking of blocker tooth ramps (48-54). The composite friction material is formed to be resilient in direction normal to its friction surface (76b), is cut into segments (76), is bonded to a frustoconical surface (62) in a manner preseving the resiliency and with the segments circumferentially spaced apart, and is configured to control engagement force thereon in a range of 150-300 pounds per square inch (10-20 Kg/cm 2 ).

This is a continuation of copending application(s) Ser. No. 07/174,475filed on Mar. 28, 1988 now abandoned.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. applications Ser. No. 150,355, filedJan. 29, 1988 and Ser. No. 174,277, filed Mar. 28, 1988 and now U.S.Pat. No. 4,844,218. Both of these applications are assigned to theassignee of this application.

1. Field of the Invention

This invention relates to liquid cooled, frictionally engaged, energyabsorbing devices such as clutches and brakes. More specifically, theinvention relates to an openly porous, resilient friction material andto a method of affixing the material to a support member.

b 2. Background of the Invention

Openly porous carbon/carbon composite, friction material formed ofcarbon fiberous substrate coated with pyrolytic carbon by chemical vapordeposition (CVD) is known in the prior art as may be seen by referenceto U.S. Pat. Nos. 4,291,794 and 4,700,823. The disclosures of thesedocuments are incorporated herein by reference.

Blocked, change gear transmissions of the single and compound type arealso known in the prior art as may be seen in U.S. Pat. Nos. 3,983,979;4,141,440; 4,176,736; and 4,703,667. The disclosures of these documentsare also incorporated herein by reference.

Blocker-clutch assemblies used in these change gear transmissionsinclude first and second positive or jaw clutches which are axiallymoved between engaged and disengaged positions to effect gear changes.Each assembly includes a fictionally engagable blocker ring whichprevents asynchronous engagement of the jaw clutches in response toinitial engaging movement thereof. The blocker ring is supported by thefirst jaw clutch for limited rotation relative thereto and includes afriction surface which engages a second friction surface, secured forrotation with the second jaw clutch, in response to the initial engagingmovement of the jaw clutches. If the jaw clutches are rotating atdifferent speeds during the initial engaging movement thereof, thefrictional engagement effects limited rotation of the blocker ring to aposition blocking engagement of the jaw clutches until substantialsynchronization of the jaw clutches is achieved.

The above described blocker-clutch assemblies have greatly reduced thecomplexity and effort required to effect gear changes. However, forvarious surmised reasons the blocker rings have been known toprematurely move to the unblocking position before the jaw clutchesreach synchronism or substantially synchronous speeds, thereby allowingasynchronous engagement of the jaw clutch teeth with resultant excessivewear thereto and in some cases failure of the jaw clutches.

SUMMARY OF THE INVENTION

An object of the invention is to provide an openly porous, resilientfriction material for a friction energy absorbing device.

Another object of the invention is to provide such a friction materialfor friction means in synchronizer or blocker assemblies used in stepratio transmissions.

According to a feature of the invention, an energy absorbing device, asdisclosed in U.S. Pat. Nos. 4,291,794 and 4,700,823, includes at leasttwo relatively rotatable members with confronting function surfacesengagable to retard the relative rotation; an openly porouscarbon/carbon composite material affixed to at least one of the membersfor defining at least one of the friction surfaces, the materialincluding a substrate defined by a carbon fiberous material woven into asingle layer substrate or fabric and coated with carbon depositedthereon by chemical vapor deposition process to a density of 0.3 to 1.3g/cc; a liquid coolant in communication with the surfaces; and anactuator means for effecting frictional engagement of the surfaces. Theinvention is characterized by the fiberous material and weave beingformed to provide the substrate with resiliency in a direction normal tothe plane of the weave before and after the chemical vapor depositionprocess; and the composite being affixed to the one member in a mannersubstantially preserving the resiliency.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is shown in the accompanyingdrawings in which:

FIG. 1 is a sectional view of a blocker-clutch assembly comprising anenvironment for use of the invention;

FIGS. 2-5 illustrate features of the assembly in FIG. 1;

FIGS. 6A-6C respectively illustrate the blocker-clutch assembly in aneutral or nonselected position, in a preselected position, and in anengaged position;

FIGS. 7-8 illustrate the configuration and position a carbon/carboncomposite friction material according to the invention; and

FIGS. 9-10 are enlarged photographic plan views of the friction surfaceof the material.

DETAILED DESCRIPTION OF THE DRAWINGS

Prior to proceeding with the detailed description, definitions of a fewtechnical terms are provided to facilitate a clearer understanding ofthe invention.

1. Pyrolytic carbon composite material--a carbon fiberous substratecoated or densified with pyrolytic carbon by a chemical vapor deposition(CVD) process.

2. Substrate--an assemblage of carbon fibers or filaments.

3. Filament--a fiber whose aspect ratio (length to effective diameter)is for all practical purposes infinity, i.e., a continuous fiber.

4. Fiber--relatively short lengths of very small cross-sections whichmay be chopped filaments (ref., Engineers' Guide to Composite Materials,American Society of Metals, Metals Park, Ohio 44073, Copyright 1987).

5. Strand--a bundle of continuous filaments combined in a single compactunit without twist (ref., Engineers' Guide to Composite Materials,American Society of Metals, Metals Park, Ohio 44073, Copyright 1987).

6. Yarn--an assemblage of twisted fibers or strands to form a continuousyarn or spun yarn suitable for use in weaving (ref., Engineers' Guide toComposite Materials, American Society of Metals, Metals Park, Ohio44073, Copyright 1987).

7. Bonding material--elements or substances capable of holding twomaterials together primarily by surface attachment, e.g., adhesives orbrazings.

8. Adhesion--the state in which two surfaces are held together at aninterface by forces or interlocking action or both.

9. Mechanical Adhesion--adhesion between surfaces in which the adhesiveholds the parts together by interlocking action.

10. Carbon--herein the term carbon includes graphite unless the termgraphite is explicitly used.

11. Total Porosity--includes open and closed pores or voids in thecomposite material. Open pores are open to the surface of the compositeand may extend completely through the composite.

12. Synchronizer--a device having blocker means for preventingasynchronous engagement of jaw or spline teeth of positive clutchmembers, and friction means operative to effect engagement of theblocker means and to generate sufficient torque during most operatingconditions to drive the positive clutch members toward synchronism.

13. Blocker--a device similar to a synchronizer but not operative duringmost operating conditions to generate sufficient torque to effectivelydrive the positive clutch members toward synchronism. Blockers of thegeneral type disclosed herein are known in the art as may be seen inreference to previously mentioned U.S. Pat. Nos. 3,983,979; 4,141,440;4,176,736; and 4,703,667.

Referring now to FIGS. 1, 2, therein is illustrated a blocker-clutchassembly 10 having first and second positive clutch members 12,14 and ablocker mechanism 16 for preventing asynchronous engagement of theclutch members which are respectively connected to a shaft 20 and a gear18. Gear 18 and shaft 20 may form part of a 4×3 compound transmissionsuch as the twelve forward speed, semi-blocked splitter type compoundtransmission disclosed in U.S. Pat. No. 4,703,667. Therein shaft 20would be a transmission main shaft disposed at an extension of its leftend into a main transmission section having four change speed ratios.Gear 18 would be a constant mesh splitter gear disposed in an auxiliarytransmission section.

Clutch member 12 is provided with internal splines 22 which are disposedwith corresponding external splines 24 provided on shaft 20 forinterconnecting clutch member 12 to the shaft for rotation therewith.The cooperating splines permit clutch member to freely slide axiallyrelative to shaft 20. A stop ring 26 is seated within a suitable grooveformed in the external periphery of the shaft and disposed forcontacting clutch member 12 and limiting rightward axial movementthereof. Clutch member 12 is resiliently urged rightward by a spring 28which reacts at its left end against a spring seat 30 secured to shaft20 in a manner similar to stop ring 26.

Clutch member 12 is provided with external spline teeth 32 thereon whichare adapted to meshingly engage internal spline teeth 34 of clutchmember 14 provided on gear 18. Teeth 32 of clutch member 12 are tapered,as at 36, in a manner similar to the leading edge 38 of teeth 34 on gear18. The tapered conical surface defined by the tapered leading edgesextends at an angle of between 30° and 40° relative to the longitudinalaxis of the shaft. The exact degree of taper and the advantages thereofare explained in detail in U.S. Pat. No. 3,265,173.

A selected number, herein three, of external spline teeth 32 arepartially removed for permitting the presence of a blocker ring 40 ofthe blocker mechanism which is further described hereinafter. Suchpartial removal leaves three axially shortened blocker tooth portions 42for cooperating with blocker ring 40. Preferably, the tooth portions aredisposed in a common plane and circumferentially spaced equal distancesapart; however, an asymmetrical arrangement such as disclosed in U.S.Pat. No. 4,703,667 may be used in some applications. The blocker ringcomprises a nondeformable ring encircling clutch member 12. The ring, asmay be seen by also referring to FIGS. 3-5, includes an appropriatenumber, herein three pairs, of radially inwardly extending projections44,46 which, when properly positioned, mate with external spline teeth32. Each pair of projections 44,46 have a total circumferentialdimension less than the corresponding circumferential spaces defined bypartially removing the tooth portions, thereby allowing limitedclockwise and counterclockwise rotation of the blocker ring relative toclutch member 12 from a position seen in FIG. 3 wherein the spacesbetween tooth projections 44,46 align with tooth portions 42. Contact ofthe sides or flanks of either tooth projection 44,46 with the sides orflanks of spline teeth 32 on either side of the space provided by thepartial tooth removal will limit such relative rotation and causeblocker ring 40 to rotate with clutch member 12. The space between eachinwardly projecting tooth pair 44,46 has a clearance distance wider thanthe corresponding circumferential dimension of tooth portions 42 so thatwhen properly aligned at synchronism (or more accurately when therelative speeds of blocker ring 40 and clutch member 12 crosssynchronism) the tooth projections 44,46 will straddle tooth portions 42and clutch member 12 can move axially through but not past blocker ringto effect engagement with spline teeth 34 of gear 18.

As may be seen in FIGS. 3-5, the end faces of tooth projections 44,46,which function as blocker teeth, are tapered or ramped as at 48,50. Theend face of each tooth portion 42 is also preferably provided withtapers or ramps 52,54 corresponding with tapers or ramps 48,50. Theangles 56 of the ramps 48-54 are selected such that blocking teeth 44,46and tooth portions 42 remain in proper blocked position when unshown butpreviously mentioned main transmission section at the left end of shaft20 is not in neutral, but will tend under a contacting force, such asthe force provided by spring 28, to cause the blocker and clutch memberto assume a nonblocking position when the main transmission is inneutral and the gear 18 has been selected for engagement. Such ramps areknown in the art as sensor unblocking ramps. Ramp angles 56 of about15°-25°, preferably 20°, relative to a plane P normal to the axis ofrotation of shaft 20 have proven highly satisfactory for most knownsemi-blocked transmissions.

As described in greater detail by reference to U.S. Pat. Nos. 3,921,469and 3,924,484, the radially inner side of blocker ring 40 may beprovided with a groove 58 which receives a split, annular, resilientring 60. Ring 60 is normally of slightly less internal diameter than theexternal diameter of clutch member teeth 34 so that when the parts arein the assembled condition, ring 60 is distorted slightly outwardly tothereby exert a light but definite resilient clamping pressure againstthe external surfaces of teeth 34. Inasmuch as ring 60 fits looselywithin the walls of groove 58, the resilient clamping pressure effects asignificant resistance to axial movement between the blocker ring andclutch member but only an insignificant resistance to relative rotativemovement therebetween.

Blocker ring 40 includes a generally outward facing frustum of a coneshape or frustoconical surface 62 positioned to frictionally engage agenerally inwardly facing frustum of a cone or frustoconical surface 64on a radially inner wall of gear 18 in response to initial axialengaging movement of gear 18 leftward by a shift fork 66 schematicallyillustrated in FIGS. 6. The axial drag provided by resilient ring 60resists axial movement of blocker ring 40 relative to clutch member 12which is biased rightward by spring 28. Accordingly, ring 60 functionsas a pre-energizer ring whose axial drag effects initial engagement ofthe surfaces 62,64 prior to axial movement of the blocker ring 40. Astop ring 68 limits movement of blocker ring 40 away from frustoconicalsurface 64 when gear 18 is moved rightward to effect disengagement ofpositive clutch members 12,14.

With respect to FIGS. 2-5 and assuming shaft 20, clutch member 12, andgear 18 are normally driven in a clockwise direction (arrow A in FIG.2), it is apparent that a nonsynchronous condition comprising gear 18rotating faster than shaft 20 and clutch member 12 will cause blockingring 40 to tend to rotate clockwise a limited amount relative to clutchmember 12 as soon as frustoconical surfaces 62,64 engage. Initialengagement of surfaces 62,64 is, of course, in response to initialengaging movement of gear 18 by shift fork 66 and the axial dragprovided by per-energizer ring 60. Shift fork 66 is connected to apiston 70 in an actuator 72 which receives pressurized air for movingthe piston to and fro in known manner. The torque applied to blockerring 40 by the initial frictional engagement due to the drag ofpre-energized ring, through relatively, small is sufficient to axiallyalign ramps 48 of the blocker tooth projections 44 with ramps 52 oftooth portions 42 prior to axial engagement of the ramps. Once the rampsengage, the force of spring 28 is transmitted through the interface ofthe ramps to increase the engaging force of the friction surfaces andthereby proportionally increase the blocking torque which is counter tothe unblocking torque provided by ramps 48,52. In theory, this increasedblocking torque is sufficient to maintain blocking engagement of theramps until clutch members 12,14 cross synchronism.

Blocker-clutch assembly 10, as thus far described, is generally known inthe prior as may be seen by reference to previously mentioned U.S. Pat.No. 4,703,667. Such assemblies provide for preselection of the ratiogears they are associated with, e.g., the actuating means (shift fork 66and piston 72) for engaging the positive clutch members 12,14 may befully displaced prior to synchronism therebetween. Actual engagement ofthe positive clutch members occurs at a later time, as may be seen byreference to FIGS. 6A-6C. Briefly, FIG. 6A illustrates a neutral ornonselected position of blocker-clutch assembly 10. FIG. 6B illustratesa preselected position wherein gear 18, clutch member 14, shift fork 60,and piston 72 are fully displaced with clutch member 12 moved leftwardagainst the bias force of spring 28 and with frustoconical surfaces62,64 frictionally engaged to maintain a blocking position untilsynchronism is crossed do to manual or automatic means changing thespeed of shaft 20 and/or gear 18. Such means are known and are typicallyprovided by changes in the speed of a prime mover connected to shaft 20and/or by use of a brake connected to the shaft or gear. When anunblocking condition occurs, as the clutch members cross synchronism,the biasing force of spring 28 moves or fires clutch member 12 intoengagement with clutch member 14. Since relatively high synchronismcrossing rates often occur, spring 28 must provide sufficient force toquickly move clutch member 12 into engagement. FIG. 6C illustrates theengaged position of the positive clutch members.

Now with respect to the present invention, it is known, as disclosed inU.S. Pat. No. 4,703,667, that blocker-clutch assemblies havingunblocking ramps, such as ramps 48-54, have a tendency under certaindynamic operating conditions to prematurely unblock or crash and allownonsynchronous engagement of clutch members 12,14. Hereinafter isdisclosed an improved friction material configuration at the interfaceof the frustoconical surfaces which has, to date, completely solved thepremature unblocking or crash problem while at the same timesubstantially reducing manufacturing cost of the blocker-clutchassemblies.

By reference now to FIGS. 7-10, therein is disclosed a carbon/carboncomposite friction material 74. FIGS. 9, 10 are enlarged photographicplan views of material 74. FIG. 9 shows the texture and porosity of thefriction surface of the material prior to testing and FIG. 10 shows thefriction surface after crash free testing equal to over three lifecycles of blocker-clutch assembly 10. FIGS. 7, 8 illustrate theconfiguration and position of the material on blocker ring surface 62.

The material 74 is preferably formed of a single woven layer substrateof carbon fibers coated or infiltrated by chemical vapor deposition(CVD) process with pyrolytic carbon. The fibers may be formed of manyknown materials, but are preferably formed of carbonized rayon orpolyacrylinitrite (PAN). Carbon filaments may be used in lieu of fibersprovided the weave of the fabric is sufficiently resilient in directionsnormal to the plane of the fabric, i.e., direction normal to thefriction plane of the material when it is in use. Acceptable CVDprocesses are taught in U.S. Pat. Nos. 4,291,794 and 3,944,686; thefirst patent teaches a batch process and the second a continuousprocess. The composite may have a density range of 0.3 to 1.3 gm/ccafter the CVD process and prior to bonding to surface 62. However,material on the low end of this range may have a higher wear rate.Material on the high end of the range is currently more expensive andmay tend to be too rigid for optimism performance. Accordingly, a rangeof 0.7 to 1.1 gm/cc is considered to be some what more optimum.

Excellent performance has been obtained with materials spec'd to have adensity of 0.8 to 1.0 gm/cc and, as tested, measured to have a densityof about 0.84 gm/cc.

Manufacturing specifications for this material require the fibers to bebased on PAN filaments chopped and spun into yarn; the yarn weight to be2/10 worsted count; the fabric weave to be 2×2 equally tensioned basketsquare weave at 18 to 22 pairs per inch (2.54 cm); the density to be 0.8to 1.1 gm/cc by CVD densification at temperatures not to exceed 1,200°C.; and the thickness to be 0.045 inches (0.11 cm). The texture of thedensified or finished material is substantially the same to the nakedeye as the woven fabric substrate. The finished material is relativelyflexible; is relatively resilient in the previously mentioned directionnormal to the plane of the fabric with such resiliently being attributedto the use of spun yarns, weave, and density; and is openly porous withmany to the pores being through pores. Carbon/carbon composite materialscomprised of substrates formed of woven carbon fibrous yarns(particularly, yarns of twisted carbon fibers) coated or densified withpyrolytic carbon by CVD process to densities less than 1.3 gm/cc haveexhibited greater resiliency in all directions than do compositematerials comprised of substrates for of comparable amounts of wovencarbon fibrous strands coated or densified with carbon by CVD process tocomparable densities.

Minimum waste of material 74 is achieved by cutting the material intopolygonal segments 76 which may be circumferentially spaced apart whenaffixed or bonded to a support member such as surface 62 of blocker ring40. Alternatively, the segments may abut each other to define acontinuous friction ring surface. When the segments arecircumferentially spaced apart, as illustrated in FIG. 7, the leadingedges 76a of the segments may be disposed oblique to the direction ofrotation of friction surface 76c defined by segments 76 to facilitaterapid wiping of excess oil (cooling fluid) off mating surfaces 64,thereby quickly achieving maximum or design coefficient of friction atthe interface of friction material surface 76c and surface 64 inresponse to initial engagement due to the force transmitted bypre-energizer ring 60. The segments are preferably cut intoparallelograms and bonded to blocker ring surface 62 with sides 76b ofthe material generally oriented parallel to planes extending normal tothe axis of rotation; however, such orientation is not believed to becritical. Further, three substantially equally spaced segments arepreferred.

Excellent bonds of the material to surface 62 have been achieved usingnitrile-phenolic adhesives which are well known in the art. Suchadhesives readily withstand operating temperature peaks in the range of400° F. (200° C.) for short periods of time. For applications producinghigher temperatures, other bonding materials are suggested, such asdisclosed in U.S. patent application Ser. No. 150,355, filed Jan. 29,1988.

Resiliency preserving bonding of the composite material to blocker ring40 with nitrile phenolic has been obtained by the following method:

1. cutting the material into conveniently handled sizes,

2. heating the material to about 150°-180° F. (65° to 85° C.),

3. rolling the adhesive in sheet form on the material,

4. shearing or cutting the material with adhesive into segments ofdesired shape and size,

5. placing the blocker ring in a fixture, positioning the adhesive sideof the segments on support surface 62, and applying a relatively evenlydistributed pressure of about 200 pounds per square inch (45 Kg/cm²) tothe friction side of the material,

6. heating the fixture and material therein in a convection oven forabout 40 minutes while maintaining the force substantially unchanged.

The adhesive used in the above example was B. F. Goodrich Plastilock 601having an 8 mil. (0.2 mm) thickness.

To prevent loss of the material's resiliency it is important curing thebonding process to limit penetration of the adhesive into the openporosity of the material and to limit the pressure applied to thematerial while heat curing the adhesive. As may be deduced, adhesivepenetration is readily controlled by stringent control of the amount ofadhesive and/or stringent control of the pressure applied to thematerial. Excessive bonding pressure tends to extrude even correctlyapplied amounts of the adhesive deeply into the pores of the material.Further, excessive bonding pressures tend to crush or compact thematerial with resultant loss of resiliency and porosity. Accordingly,proper bonding pressures are readily determined by bearing in mind thatthe pressure should be sufficient to firmly hold the material during thebonding process without overly compacting or crushing the material.

Further with respect to porosity and resiliency, the spun yarns andweave of the yarns provide an openly porous substrate or fabric which isrelatively resilient in the direction normal to the weave of the fabric.A substantial portion of the substrate open porosity and resiliency isretained by the composite material by limiting CVD coating ordensification of the substrate to the range of 0.3 to 1.3 gm/cc(preferably 0.8 to 1.1) gm/cc. Further, the open porosity and resiliencyof the composite material in the area of its friction surface ismaintained during the bonding process by using volumes of adhesive thatare less than the open porosity volume of the composite, and by limitingthe magnitude of the bonding process pressure for minimizing crushingthe composite material and for maintaining the open porosity volume ofthe composite material greater than the volume of the adhesive, wherebythe volume of the open pores adjacent to the bond side of the compositematerial consumes the adhesive while the pores adjacent to the frictionside remains free of the adhesive. Bonding pressures less than 250pounds per square inch (17.6 Kg/cm²) are considered adequate for mostcarbon/carbon composite materials acceptable for use with blocker-clutchassembly 10.

It has been discovered that premature unblocking can be effectivelyeliminated by controlling unit loading on the friction surface 76c ofmaterial 74 within a range of 150-300 pounds per square inch (10-20Kg/cm²). Since such unit loading in an assembly such as blocker-clutchassembly 10 is primarily a function of the biasing force of spring 28and since the force of spring 28 must be within a rather narrow range,unit loading has been controlled by tailoring or configuring the surfacearea 76c of material 74. By way of example, crash free operation hasbeen obtained in tests of blocker-clutch assembly 10 using threeparallelogram shaped segments 76 having a combined friction surface areaof 1.17 square inches (7.55 cm²). In this example, cone surfaces 62,64have an angle of about 10° and a mean diameter of about 4.35 inches (11cm), ramps 48-54 have an angle of about 20°, and spring 28 provides abiasing force of about 50 pounds (27 Kg) when compressed in FIG. 62.

In the blocker-clutch assembly of this example, the combined frictionsurface areas 76c constitute a 83% reduction in total friction materialsurface area relative to the blocker-clutch assembly disclosed in U.S.Pat. No. 4,703,667 and the pressure at the interface of the combinedsurface areas 76c is 210 pounds per square inch (14.8 Kg/cm²).

A preferred embodiment of the invention has been disclosed forillustrative purposes. Many variations and modifications of thepreferred embodiment are believed to be within the spirit of theinvention. The following claims are intended to cover the inventiveportions of the preferred embodiment and modifications believed to bewithin the spirit of the invention.

What is claimed is:
 1. A method of providing a rigid member with aresilient friction surface defined by a carbon/carbon composite materialcomprising a substrate defined by a carbon fibrous material woven into asingle layer of fabric coated with carbon deposited on the fibrousmaterial by chemical vapor deposition process; the method characterizedby the steps of:forming the fibrous material of yarns defined by carbonfibers; weaving the yarns into an openly porous fabric having resiliencyin a direction normal to the plane of the fabric, said resiliency beinggreater than the resiliency of a comparable weave formed of carbonfibrous strands; limiting the carbon coating of the fibers for retaininga given amount of the open porosity and resiliency of the fabric;cutting the composite material into segments; affixing the compositematerial to the member in a manner preserving the composite materialsopen porosity and resiliency at least at the surface of the compositematerial by the steps of: sandwiching an adhesive between the member andat least three circumferentially spaced apart segments of the material,the volume of the adhesive being less than the open porosity volume ofeach associated segment; applying a substantially evenly distributedpressure to the friction surfaces of the segments for effectingextrusion of the associated adhesive into the open pores of thesegments; limiting the magnitude of the pressure for minimizing crushingof the composite material and for maintaining the open porosity volumeof each segment greater than the volume of the associated adhesive;applying heat to the segments, the adhesive, and the member foreffecting extrusion of the adhesive into the open pores adjacent theretoand for curing of the adhesive; and maintaining the limited pressurewhile applying the heat.
 2. The method of claim 1, comprising the stepsof:coating the composite material to a level providing a compositedensity of 0.8 to 1.1 gm/cc; limiting said pressure to a maximum of 250pounds per square inch of segment surface area.
 3. A clutch assemblyincluding a first frustoconical surface nonrotatable relative to a firstjaw clutch; a blocker ring mounted for a limited degree of rotationrelative to a second jaw clutch and having a second frustoconicalsurface frictionally engagable with the first surface in response toinitial, axial engaging movement of the jaw clutches by an actuatormeans; a liquid coolant in communication with the friction surfaces; theblocker ring having means operative to block asynchronous engagement ofthe jaw clutches; characterized by;at least three friction materialsegments bonded to at least one of the frustoconical surfaces with theirleading and trailing edges substantially equal circumferential distancesapart, said segments being formed of an openly porous carbon/carboncomposite material comprising a substrate defined by a carbon fibrousyarns woven into a single layer of fabric substrate and coated withcarbon deposited thereon by chemical vapor deposition process, saidfibrous material and weave being formed to provide the substrate withresiliency in a direction normal to the plane of the weave before andafter the chemical vapor deposition process, said resiliency beinggreater than the resiliency of a comparable weave formed of carbonfibrous strands coated with comparable amounts of carbon by chemicalvapor deposition, and the composite being bonded to the one member in amanner substantially preserving said resiliency.
 4. The assembly ofclaim 3, wherein the yarns are formed of twisted carbon fibers.
 5. Theassembly of claim 4, wherein the density of the composite material is inthe range of 0.7 to 1.1 g/cc.
 6. The assembly of claim 5, wherein theengaging pressure on the friction surface of the segments is in therange of 150 to 300 pounds per square inch.
 7. A clutch assemblyincluding a first frustoconical surface nonrotatable relative to a firstjaw clutch; a blocker ring mounted for a limited degree of rotationrelative to a second jaw clutch and having a second frustoconicalsurface frictionally engagable with the first surface in response toinitial, axial engaging movement of the jaw clutches by an actuatormeans; a liquid coolant in communication with the friction surfaces; theblocker ring having means operative to block asynchronous engagement ofthe jaw clutches; characterized by:at least three friction materialsegments formed of a carbon/carbon composite material having a densityof 0.3 to 1.3 g/cc and formed from a carbon fiberous substrate coatedwith carbon deposited thereon by chemical vapor disposition and bondedto at least one of the frustoconical surfaces with their leading andtrailing edges being substantially equal circumferential distancesapart.
 8. The device of claim 7, wherein the density of the compositematerial is in the range of 0.7 to 1.1 g/cc.
 9. The assembly of claim 8,wherein the actuator means includes means for limiting engagement forcebetween the surface of the composite friction material and thefrustoconical surface of the other member to a range of 150-300 poundsper square inch of the friction material surface.
 10. The device ofclaim 9, wherein the engaging pressure is in the range of 175 to 245pounds per square inch.